October's birthstone is opal. It is also tourmaline. Two stones, and between them they cover most of the visible spectrum — which is convenient, because October is the month with the least agreement about what its colour is supposed to be.
Opal is the older entry and the one most people mean. It also carries the strangest piece of baggage of any stone on the list: for most of the nineteenth century, a great many Europeans believed it was unlucky. That belief has a traceable start date, and it is not ancient.
The unlucky opal was invented by a novelist
Before 1829, opal had a good reputation. The Romans prized it. Pliny the Elder wrote about it admiringly. There is no long folk tradition of opal as a cursed stone.
Then Walter Scott published Anne of Geierstein. In it, the Lady Hermione wears an opal that flashes when she is happy, dims when she is not, and is destroyed — along with her — when holy water touches it. The novel was enormously popular. Within about a year, opal sales across Europe reportedly collapsed, and the stone spent the rest of the century being avoided by people who could not have told you why.
It took the discovery of the Australian fields later in the century, and a lot of deliberate promotion, to undo it. The superstition is younger than the steam locomotive and it came out of a novel. That is the entire provenance.
What opal actually is
Opal is hydrated silica — silicon dioxide with water in it, sometimes as much as twenty per cent by weight. Unlike almost every other gem, it has no crystal structure. It is not a crystal at all.
The play-of-colour was a genuine mystery until electron microscopy in the 1960s settled it. Precious opal is built of microscopic silica spheres packed in a regular three-dimensional grid. Light entering that grid diffracts, and the size of the spheres determines which wavelengths come back. Small spheres return blue and violet. Larger ones return orange and red — which is why red flash is the rarest and the most expensive.
Where the spheres are packed irregularly, you get common opal: the same material, no fireworks.
Living with opal
Two honest cautions, because opal is the one birthstone that genuinely asks something of you.
It is soft — around 5.5 to 6.5 on the Mohs scale, softer than quartz, which means ordinary household dust can scratch it. And because of the water content, some opal can craze: fine surface cracks that appear if the stone is dried out by heat, direct sun over long periods, or an ultrasonic cleaner.
This is not a reason to avoid it. It is a reason to wear it as a necklace or earrings more often than as an everyday ring, and to clean it with a soft damp cloth and nothing else.
Tourmaline: the stone that pulls ash
Tourmaline joined the list later and is really a family rather than a single stone — elbaite is the species most gem tourmaline belongs to. It occurs in more colours than any other gem material, sometimes several in one crystal. Watermelon tourmaline, pink at the core and green at the rind, is a single crystal that changed its chemistry as it grew.
Its odd property is electrical. Tourmaline is pyroelectric and piezoelectric: heat it or squeeze it and it develops a charge at opposite ends of the crystal. Dutch traders in the eighteenth century knew this before anyone had explained it — they used warm tourmaline to draw the ash out of their pipes, and called the stone aschentrekker, ash-puller.
Which one is yours?
Both, and there is no authority to appeal to. The modern birthstone list is a trade standard agreed by American jewellers in 1912 and revised since; it differs between countries and it was written by people selling jewellery. Opal is the traditional October stone. Tourmaline was added because opal is fragile and shops wanted something for the same month that could take daily wear.
That is a practical reason, not a mystical one, and it is worth knowing that is where these lists come from.
What we make for October
Our opal is natural African opal, and it sits in The Zodiac Circle — a single disc with your Chinese zodiac animal worked in relief in gold, the rest of the ring left dark so the opal carries all the light. Ten of the twelve animals are set with it.
The plainer option is Month in Colour, one baguette stone on a fine chain in solid gold-plated 925 silver — not plated brass, which is the usual way to make a necklace look like that one. The October stone is opal white. It is cubic zirconia cut to the birthstone colour, not natural opal, and we say so on the product page rather than in grey type at the bottom.
Both are made after you order, so allow up to ten days.
All twelve months, and what each stone actually is →
The twelve animals, and why your year might not be the one you think →
A birthstone is a date, not a diagnosis. Nothing here treats, prevents or cures anything.